Many real-world problems ask you to deal with rates. Rates involve how
fast, how long, and how many of something happens. Rates are expressed as
"how many per how long" as in 10 miles per hour. Per means divide,
so 10 miles per hour is 10 miles/hour.

Write 10 miles so you can cancel units later
hour

You could also have "gallons per hour" or even "peanuts per minute". In
this lesson we are going to deal with distance (how many miles, feet,
inches) using the following formula where r is the rate, t is the time and
d is the distance:

r x t = d

This means that r = d/t and t = d/r. You can memorize all three formulas,
but I think it is easier to remember just one formula (r x t = d) and
then use algebra if you want to solve for r or t.

To find

Solve for

Units will
be

How far

d

miles, feet, km, etc.

How fast

r

miles per hour, feet per second, etc.

How long

t

hours, minutes, seconds, etc.

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Example 1: A car goes 30 miles per hour for 2 hours. How far does
it go?

Start by writing the formula: r x t = d. What are we asked for?
We are asked "how far." We must solve for d. So r = 30
miles/hour, t = 2 hours.

d = 30 miles x 2 hours = 60 miles
hour

Notice that the "hours" with t cancel with the denominator of
r so that the resulting units are just "miles".